Waste heat recovery system

ABSTRACT

The invention relates to a waste heat recovery system (1) comprising a working fluid circuit (18), having a heat exchanger which is connected in an exhaust gas line (4) of an internal combustion engine (2). The heat exchanger is part of the working fluid circuit (18) together with an expansion machine (20) which has at least one working fluid bypass (21) that is controlled by a valve. According to the invention, a waste heat recovery system (1) is provided with improved functionality. This is achieved in that the valve is a directional valve which connects a fluid inlet (36) to an expansion machine fluid outlet (37) and/or a bypass fluid outlet (38), in particular a 3/2-way valve (22), and the connection of the fluid inlet (36) to the expansion machine fluid outlet (37) is leakage-free relative to the bypass fluid outlet (38), whereas the connection of the fluid inlet (36) to the bypass fluid outlet (38) exhibits leakages with respect to the expansion machine fluid outlet (37).

BACKGROUND OF THE INVENTION

The invention relates to a waste-heat recovery system with a workingfluid circuit having a heat exchanger connected into an exhaust-gas lineof the internal combustion engine, wherein the heat exchanger is part ofthe working fluid circuit with at least one expansion machine which hasa bypass controlled by a valve.

A waste-heat recovery system of said type is known from DE 10 2013 021251 A1. Said waste-heat recovery system has a working fluid circuitwhich has the conventional components. These are, substantially, anevaporator connected into an exhaust-gas line of an internal combustionengine, and expansion machine with the bypass control by a valve, acondenser, and a working fluid pump. By means of the bypass control bythe valve, the expansion machine can be switched into a torque-freestate. Here, the bypass and the valve are arranged within or integratedinto the expansion machine.

SUMMARY OF THE INVENTION

The invention is based on the object of providing a waste-heat recoverysystem which is improved with regard to its function.

Said object is achieved in that the valve is a directional valve, inparticular 3/2 directional valve, which connects a fluid inlet to anexpansion machine fluid outlet and/or to a bypass fluid outlet, and inthat a connection made between fluid inlet and expansion machine fluidoutlet exhibits no leakage to the bypass fluid outlet. Said 3/2directional valve can conduct the working fluid flowing and the workingfluid circuit either via the expansion machine or, pass the expansionmachine, directly to a condenser provided in the working fluid circuitdownstream of the expansion machine. It is a first object of said 3/2directional valve, for example in the case of a mechanical connection ofthe expansion machine to a crankshaft of the internal combustion engine,and in the presence of a torque demand of “zero”, to conduct the workingfluid directly to the condenser, such that the expansion machine is notdriven by the working fluid and therefore outputs no torque to thecrankshaft. It is a second object of the 3/2 directional valve toprotect the expansion machine if the working fluid is in a wet steamrange. During expander operation, in which the expansion machine isflowed through in the intended manner by the working fluid, leakage inthe direction of the bypass, which would constitute an impairment of theefficiency of the expansion machine, is prevented according to theinvention. By means of this embodiment, the function of the waste-heatrecovery system is improved.

In a refinement of the invention, a connection made between fluid inletand bypass fluid outlet exhibits leakage, with a leakage quantity, tothe expansion machine fluid outlet. Here, in a further embodiment of theinvention, the leakage quantity to the expansion machine fluid outlet isless than 10% of the maximum volume flow of the working fluid throughthe working fluid circuit, preferably less than 1% of the maximum volumeflow. Such a minimum leakage quantity is expedient because, in this way,the expansion machine is for example heated during a commencement ofoperation of the waste-heat recovery system, or in the event oftemporary bypassing the expansion machine, cooling of the expansionmachine is prevented. “Permanent lubrication” of the expansion machineis also ensured. This embodiment also sustainably improves the functionof the waste-heat recovery system.

In a refinement of the invention, the 3/2 directional valve has a slide(in the form of a piston) with two opposite switching positions that canbe assumed by the slide. Here, the switching positions of the slide canbe defined or occupied by a slide seat on the bypass fluid outlet and anexpansion machine outlet seat at the expansion machine fluid outlet.This is one possible embodiment, in which a short stroke of the slidecan be realized, whereby, in turn, a simple, inexpensive design of anactuating element for the adjustment of the slide can be realized.

In a second embodiment, the switching positions of the slide may bedefined by a slide seat on the bypass fluid outlet and, as a substitutefor the single expansion machine outlet seat at the expansion machinefluid outlet, by an overlap gap assumed by the slide relative to a slidehousing. This embodiment is basically similar in terms of function tothe first embodiment, wherein here, the required stroke of the slide islonger owing to the overlap that is to be realized.

In a further configuration of the invention, the 3/2 directional valvehas a slide housing and a slide which is displaceable in said slidehousing axially counter to the force of a spring, which slide has apermanent flow connection to the fluid inlet and can be adjusted in eachcase into a flow connection with the bypass fluid outlet and with theexpansion machine fluid outlet. This is an embodiment of the 3/2directional valve realized in all conceivable configurations.

In a refinement of the invention, the bypass fluid outlet has a bypassfluid outlet seat into which an end-side slide seat of the slide can beengaged with sealing action. In this way, in a corresponding switchingposition of the slide, the absence of leakage of the fluid inlet to thebypass fluid outlet is ensured.

In a refinement of the invention, the slide seat is arranged on a slidebase wall of the slide of piston-like form (opposite the side of theconnection of an actuator switching rod), and wherein the slide basewall has at least one passage opening which permits a throttling-freethroughflow of the working fluid.

The desired leakage of the working fluid to the expansion machine outletmay be produced or set by means of corresponding play between the slideand the slide housing. Alternatively, the leakage may however also beproduced by means of a leakage throttle bore in the slide.

In a further configuration of the invention, the slide interacts with anactuator. The actuator may be designed as an electromagnet or else maybe configured or actuated in pneumatic, hydraulic or electromagnetic orsome other form.

In summary, the waste-heat recovery system configured in this way offersthe following advantages:

-   -   in turbine operation, in which the working fluid is to be        conducted entirely through the expansion machine, it is ensured        that no leakage occurs in the direction of the bypass fluid        outlet,    -   by contrast, in bypass operation, when the working fluid is        conducted through the bypass, a minimal leakage in the direction        of the expansion machine fluid outlet is set in order, for        example, to heat the expansion machine,    -   only low actuator forces are necessary, because the slide is        pressure-balanced. The actuator consequently has to overcome        only spring forces and flow forces,    -   in expander operation, it is likewise the case that only low        actuator forces are necessary, because, in this switching state,        the slide is not force-balanced, and the acting force acts with        a closing action toward the bypass fluid outlet,    -   a robust design with low acting seat forces can be implemented,        and    -   the 3/2 directional valve can be implemented inexpensively.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantageous configurations of the invention emerge from thedescription of the drawings, which gives a description of exemplaryembodiments illustrated in the figures.

In the figures:

FIG. 1 shows a schematic circuit diagram of a waste-heat recovery systemwhich has an expansion machine and a working fluid circuit, wherein thewaste-heat recovery system is installed on an internal combustionengine,

FIG. 2a shows a first exemplary embodiment of a bypass, controlled by avalve, of the working fluid circuit past an expansion machine in a firstswitching position,

FIG. 2b shows a first exemplary embodiment of a bypass, controlled by avalve, of the working fluid circuit past an expansion machine in asecond switching position,

FIG. 3a shows a second exemplary embodiment of a bypass, controlled by avalve, of the working fluid circuit past an expansion machine in a firstswitching position,

FIG. 3b shows a second exemplary embodiment of a bypass, controlled by avalve, of the working fluid circuit past an expansion machine in asecond switching position.

DETAILED DESCRIPTION

FIG. 1 shows a waste-heat recovery system 1, which is installed on aninternal combustion engine 2 which has a cooling system (not illustratedin any more detail). The internal combustion engine 2 furthermore has afresh-gas line 3 and an exhaust-gas line 4. Via the fresh-gas line 3,the internal combustion engine 2 is supplied with combustion air which,in the exemplary embodiment, is compressed by a compressor 5 of anexhaust-gas turbocharger 6, which in turn is driven by a turbine 7incorporated into the exhaust-gas line 4. A charge-air cooler 8 and athrottle flap 9 are connected downstream of the compressor 6.

The fresh gas supplied to individual combustion chambers of the internalcombustion engine 2 with a simultaneous supply of fuel, for examplediesel fuel, burns in the combustion chambers of the internal combustionengine 2, generating working power, which is output, for example via anoutput shaft 10 which is connected to the crankshaft of the internalcombustion engine 2 via a transmission, to a drive axle 11, by means ofwhich an arbitrary vehicle in which the internal combustion engine 2 isinstalled is driven. Via the exhaust-gas line 4, the mixture of fuel andfresh gas burned in the combustion chambers of the internal combustionengine 2 is ultimately discharged as hot gas into the surroundings. Theexhaust-gas line 4 is connected to the fresh-gas line 3 via anexhaust-gas recirculation line 12 with, incorporated therein, anexhaust-gas recirculation cooler 13 and an exhaust-gas recirculationvalve 14. Via the exhaust-gas recirculation line 12, exhaust gas isrecirculated in controlled fashion into the fresh-gas line 3, inparticular in order to reduce the harmful exhaust-gas emissions.Downstream of the turbine 7, an exhaust-gas aftertreatment device 15 islikewise provided for reducing the harmful exhaust-gas emissions.Further downstream, a heat exchanger in the form of a superheater 16 ofthe waste-heat recovery system 1 is incorporated into the exhaust-gasline 4, which heat exchanger can be bypassed in controlled fashion viaan exhaust-gas line bypass 17. The superheater 16 is incorporated into aworking fluid circuit 18 of the waste-heat recovery system 1—as will bediscussed in more detail below.

The internal combustion engine 2 has the abovementioned cooling systemwith a coolant circuit, which is however of no further importance of thesubject matter of the invention and is therefore not illustrated. Thecooling system serves for the cooling of the internal combustion engine2 and has a coolant cooler incorporated into the cooling circuit and acoolant pump. The coolant pump conveys the coolant through coolingchambers of the internal combustion engine 2 into the coolant cooler,which is connected at the outlet side to the suction side of the coolantpump. Also suitably incorporated into said coolant circuit are, forexample, a lubricating oil heat exchanger, a retarder heat exchanger,the charge-air cooler 8 and the exhaust-gas recirculation cooler 13.

Returning to the waste-heat recovery system 1, the latter has theworking fluid circuit 18 with the superheater 16 incorporated into theexhaust-gas line 4. Also incorporated into the working fluid circuit 18is an expansion machine 20 which is driven by the working fluid changedinto the gaseous state in the superheater 16, with expansion of saidfluid, and which outputs working power to the internal combustion engine2 or to some other machine, for example a generator. Here, the expansionmachine 20 can be bypassed via a working fluid bypass 21, which iscontrolled by a directional valve 22 formed preferably as a 3/2directional valve. Furthermore, a condenser 23 is incorporated into theworking fluid circuit 18 downstream of the expansion machine 20, inwhich condenser the working fluid is normally cooled down into theliquid state and is subsequently supplied to a working fluid pump 24.The working fluid pump 24 is for example electrically driven by a motor19 and conveys the cooled-down working fluid back to the superheater 16.Here, at the outlet side of the working fluid pump 24, a pressurecompensation tank 25 is incorporated into the working fluid circuit 18.

The abovementioned condenser 23 is in turn a constituent part of aworking fluid cooling circuit 26, which furthermore has a cooler 27. Thecooler 27 is for example arranged upstream or downstream of the coolantcooler and is flowed through by a cooling air flow which is conveyed forexample by a fan 28, which is driven directly or indirectly by theinternal combustion engine 2. Finally, an electric or electronic controldevice 29 is provided, which controls the waste-heat recovery system 1including possibly the entire internal combustion engine 2. Said controldevice 29 also serves for controlling the 3/2 directional valve 22 ofthe waste-heat recovery system 1, which valve will be discussed in moredetail with regard to its design and function in the following figures.

FIG. 2a shows the directly controlled 2/3 directional valve 22, which ispressure-balanced at least in one switching position, in a firstembodiment, and shows a switching position in which the working fluid ofthe working fluid circuit 18 is conducted to the expansion machine 20.By contrast, in the switching position of the 3/2 directional valve 22illustrated in FIG. 2b , the working fluid is conducted to the workingfluid bypass 21 and thus so as to bypass the expansion machine 20. The3/2 directional valve 22 has a cylindrical tubular slide housing 30 inwhich a slide 31 of piston-like form is adjustable axially counter tothe force of a spring 32. Said adjustment movement is effected by anactuator 33 which is fixedly connected by means of an actuator holdingdevice 34 to the slide housing 30 and which has an actuator switchingrod 35, which in turn is connected to the slide 31 for the direct axialadjustment of the slide 31. For example, the actuator 33 is formed as anelectromagnet and, when electrically energized, moves the actuatorswitching rod 35 with the slide 31 into the position illustrated in FIG.2a , whereas, when electrically deenergized, the position of the slide31 illustrated in FIG. 2b is set by means of the restoring force of thespring 32. The actuator 33 may however also for example be of pneumatic,hydraulic or electromagnetic form in other embodiments.

The slide housing 30 has a tubular and flange-mounted fluid inlet 36,which is connected to the working fluid circuit 18 at the outlet side ofthe superheater 16. Furthermore, the slide housing 30 has a likewisetubular expansion machine fluid outlet 37, which is connected directlyor indirectly to the flow inlet into the expansion machine 20. Theexpansion machine fluid outlet 37 may, like the fluid inlet 36, beconfigured as a metallic pipe connection piece, which is welded to theslide housing 30, the latter likewise being manufactured from a metallicmaterial. Furthermore, the 3/2 directional valve 22 has a bypass fluidoutlet 38, which is connected to the working fluid bypass 21. The bypassfluid outlet 38 is arranged on a closure plate 39, opposite the actuatorholding device 34, on the slide housing 30, or is a constituent part ofthe closure plate 39 and formed for example as a bypass fluid outletpipe with a throttling action set by means of the pipe diameter.

The bypass fluid outlet 38 or the bypass fluid outlet pipe has a bypassfluid outlet seat 40, in which an end-side facing slide seat 41 of theslide 31 can be engaged with sealing action and thus in leakage-freefashion. The slide seat 41 is arranged on, or formed in one piece with,a slide base wall of the slide 31 of piston-like form, wherein the slidebase wall has passage openings 45 for an unhindered throughflow of theworking fluid.

The corresponding switching position is illustrated in FIG. 2a . In thisswitching position, the working fluid flowing into the 3/2 directionalvalve 22 or the slide housing 30 via the fluid inlet 36 flows inleakage-free fashion into the expansion machine fluid outlet 37 inaccordance with the illustrated flow arrows. In the region of theexpansion machine fluid outlet 37, an encircling ring-shaped groove 42is recessed into the slide housing 30, which ring-shaped groove promotesan unhindered flow through the 3/2 directional valve 22 and, at the sametime, in the direction of the actuator holding device 34, transitionsinto an expansion machine fluid outlet seat 43 adjacent to the fluidinlet 36.

The slide 31 is displaceable with an encircling slide edge 44 into theexpansion machine fluid outlet seat 43, which is formed for example by acylindrical pipe diameter reduction of the slide housing 30. Thecorresponding switching position is, as stated above, illustrated inFIG. 2b . In this switching position, the direct passage from the fluidinlet 36 via the expansion machine outlet seat 43 and the ring-shapedgroove 42 into the expansion machine outlet 37 is blocked. At the sametime, it is however the case that the working fluid flows, in accordancewith the illustrated flow arrows, through the slide 31 of piston-likeform, and passes via the passage openings 45 directly into the bypassfluid outlet 38, because, in this switching position, the slide seat 41has been moved out of the bypass fluid outlet seat 40 and opens up aflow connection.

At the same time, in this switching position, a small leakage of themaximum volume flow of the working fluid from the fluid inlet 36 to theexpansion machine fluid outlet 37 is set, which is set by means of theplay with which the slide 31 is guided in the slide housing 30. Here,the defined leakage quantity 46 a of the working fluid passes from theslide seat 41 back to the expansion machine fluid outlet 37.Alternatively (in the case of play-free guidance of the slide 31 in theslide housing 30) or in addition, it is also possible for at least oneleakage throttle bore 47 a, illustrated only in FIG. 2b , to be providedin the slide 31 in the region of the ring-shaped groove 42. The leakagequantity 46 a of the working fluid is less than 10% of the maximumvolume flow, preferably less than 1% of the maximum volume flow.

The exemplary embodiment as per FIGS. 3a, 3b differs from that of FIGS.2a, 2b in that, here, no expansion machine fluid outlet seat 43 isprovided into which a slide edge 44 could engage in the switchingposition as per FIG. 3b . In this exemplary embodiment, the slidehousing 30 is formed with a shoulder-free internal diameter. Thus, it isalso the case in the switching position as per FIG. 3b (the switchingposition is identical to that of FIG. 2a at least in terms of function)that a leakage quantity 46 b flows from said side from the fluid inlet36 into the expansion machine fluid outlet 37. In this embodiment, too,the entire leakage quantity 46 a, 46 b of the working fluid is less than10% of the maximum volume flow, preferably less than 1% of the maximumvolume flow. Furthermore, in this embodiment, the switching travel to becovered by the actuator 33 is longer than in the exemplary embodiment asper FIGS. 2a, 2b .

It is finally pointed out that any design details illustrated in thefigures may be combined with one another within the scope of theinvention.

1. A waste-heat recovery system (1) with a working fluid circuit (18)having a heat exchanger connected into an exhaust-gas line (4) of theinternal combustion engine (2), wherein the heat exchanger is part ofthe working fluid circuit (18) with at least one expansion machine (20)which has a working fluid bypass (21) controlled by a valve, wherein thevalve is a directional valve (22) which connects a fluid inlet (36) toan expansion machine fluid outlet (37) and/or to a bypass fluid outlet(38), and wherein a connection made between the fluid inlet (36) and theexpansion machine fluid outlet (37) exhibits no leakage to the bypassfluid outlet (38).
 2. The waste-heat recovery system (1) as claimed inclaim 1, characterized in that a connection made between fluid inlet(36) and the bypass fluid outlet (38) exhibits leakage, with a leakagequantity (46 a, 46 b), to the expansion machine fluid outlet (37). 3.The waste-heat recovery system (1) as claimed in claim 2, characterizedin that the leakage quantity (46 a, 46 b) is less than 10% of themaximum volume flow of the working fluid.
 4. The waste-heat recoverysystem (1) as claimed in claim 2, characterized in that the directionalvalve (22) has a slide (31) with two opposite switching positions thatcan be assumed by the slide (31).
 5. The waste-heat recovery system (1)as claimed in claim 2, characterized in that the directional valve (22)has a slide housing (30) and a slide (31) which is displaceable in saidslide housing axially counter to the force of a spring (32), which slidehas a permanent flow connection to the fluid inlet (36) and can beadjusted in each case into a flow connection with the bypass fluidoutlet (38) and with the expansion machine fluid outlet (37).
 6. Thewaste-heat recovery system (1) as claimed in claim 2, characterized inthat the directional valve (22) has a bypass fluid outlet seat (40)configured to have an end-side slide seat (41) of the slide (31) engagedtherein with sealing action.
 7. The waste-heat recovery system (1) asclaimed in claim 2, characterized in that the slide housing (30) has anexpansion machine fluid outlet seat (43) configured to have a slide edge(44) of the slide (31) engaged therein with sealing action.
 8. Thewaste-heat recovery system (1) as claimed in claim 6, characterized inthat the slide seat (41) is arranged on a slide base wall of the slide(31) of piston-like form, and in that the slide base wall has passageopenings (45) for an unhindered throughflow of the working fluid.
 9. Thewaste-heat recovery system (1) as claimed in claim 4, characterized inthat the slide (31) interacts with an actuator (33).
 10. The waste-heatrecovery system (1) as claimed in claim 2, characterized in that theleakage quantity (46 a, 46 b) is less than 1% of the maximum volume flowof the working fluid,